Critical micellization temperature

Fig. 51 Phase diagram for PS-PI diblock copolymer (Mn = 33 kg/mol, 31vol% PS) as function of temperature, T, and polymer volume fraction, cp, for solutions in dioctyl ph-thalate (DOP), di-n-butyl phthalate (DBP), diethyl phthalate (DEP) and M-tetradecane (C14). ( ) ODT (o) OOT ( ) dilute solution critical micelle temperature, cmt. Subscript 1 identifies phase as normal (PS chains reside in minor domains) subscript 2 indicates inverted phases (PS chains located in major domains). Phase boundaries are drawn as guide to eye, except for DOP in which OOT and ODT phase boundaries (solid lines) show previously determined scaling of PS-PI interaction parameter (xodt

A critical micelle temperature or CMT is a very useful value for PEO-PPO-PEO copolymers. This arises from the fact that micellization in these copolymers is due to the dehydration of the PPO block with increasing temperature. The value of the CMT ranges from 20 to 50 °C in commercially available PEO-PPO-PEO copolymers. The CMT increases whenever the copolymer concentration is increased [19]. 

ARRHENIUS EQUATION PLOT CRITICAL MICELLE CONCENTRATION CRITICAL MICELLE TEMPERATURE Critical protein concentration,... 

Thus the logarithm of the erne can be plotted against inverse temperature to extract information on the micellization enthalpy. Equivalently, the logarithmic concentration can be plotted against the inverse critical micelle temperature (Alexandridis et al. 1994a Yang et al. 1994). 

Fig. 3.10 Logarithm of concentration vs. reciprocal of the critical micelle temperature for aqueous solutions of triblock copolymer PE02iPBOsPE02, (Booth et al. 1997 Yang et al. 1994). The unfilled data point is log(cmc) from surface tension plotted against reciprocal temperature.

Fig. 3.19 Critical micelle temperature versus the polymer concentration calculated for an aqueous solution of Pluronic P105 (PEO37PPO56PEO37) (Linse 1994b). Results from a polydisperse model (MJMn = 1.2) are shown as solid lines and for the monodisperse polymer as a dashed line. The curves for the polydisperse system are labelled in terms of the number of components representing the polydisperse polymer. Points with constant micellar volume fractions (criterion of the cmc) are represented by dotted curves, the volume fraction being indicated. Experimental data from Alexandridis et al. (1994a) are also included as filled squares.

Critical Micelle Concentration and Critical Micelle Temperature. 340... 

Another important transition of surfactants involving micelles, the critical micellization temperature (CMT), has been found to be readily amenable to study by FT-IR, largely because of the relatively high surfactant concentrations involved (>0.1 M). The CMT is concentration dependent up to concentrations of about 0.1 to 0.3 M, above which the dependence decreases significantly. The Krafft point is thus found at lower temperatures than the CMT, and can be considered the CMT at the cmc (63-65). A thermostatted transmission cell for control of the temperature of the surfactant solutions, held between CaF2 or BaF2 windows, is necessary. Automation of the entire spectroscopic CMT experiment has been described (66). 

Figure 1 Pictoral phase diagram for a typical ionic surfactant. Micellar phases exist at temperatures above the critical micellization temperature (cmt), and concentrations above the critical micellization concentration (cmc). "pseudophase" transition from spherical to rodlike micelles may also occur at low temperatures or high surfactant concentrations. Also shown are regions where hydrated solid (gel or coagel) phases and liquid crystals (lamellar or hexagonal) appear (artwork courtesy of Linda Briones).

SDS/NaCI Mixtures. The effect of temperature on the micelles formed in 70 mM SDS + NaCl solutions is presented below. Mazer et al. (14) have found that the aggregation number, N, is at a maximum for supercooled solutions below the critical micellization temperature (cmt), and decreases towards the value expected for a spherical micelle as the temperature is increased. The variations in N with temperature are dependent on the concentration of added electrolyte, with the rodlike micelles formed in high salt (0.6 M) showing large variations, and the spherical micelles formed in little (0.3 M) or no salt showing only small variations. 

Figure 17 Temperature dependence of the symmetric CH2 stretching mode at various electrolyte levels in 70 mM SDS+NaCl mixtures. Plotted in the inset are the critical micellization temperatures obtained as a function of added NaO (14Mb...

Block copolymers of 23b and alkyl methacrylates [158] and diblock copolymers of 23b with 2-(diethylamino)ethyl methacrylate (23b-DEAEM), 2-(diisopropylamino)ethyl methacrylate (23b-DIPAEM), or 2-(N-morphoHno) ethyl methacrylate (23b-MEMA) exhibited reversible pH-, salt-, and temperature-induced micellization in aqueous solution under various conditions. The micelle diameters were 10-46 nm [238]. The micelles of these hydropho-bically modified polybetaines consist of coronas from 23b and cores from polyDEAEM, polyDIPAEM, or polyMEMA. In aqueous solution, the 23b-MEMA diblock copolymers form micelles with cores of polyMEMA above an upper critical micelle temperature of about 50 °C, and reversibly betainized-DMAEM core micelles below a lower critical micelle temperature of approximately 20 °C [239]. 

There continues to be extensive interest in latexes and micellar systems. The structure of acrylic latex particles has been investigated by non-radiative energy transfer by labelling the co-monomers with fluorescent acceptor-donor systems. Phase separations could also be measured in this way. Excimer fluorescence has been used to measure the critical micelle temperature in diblock copolymers of polystyrene with ethylene-propylene and the results agree well with dynamic light scattering measurements. Fluorescence anisotropy has been used to measure adsorption isotherms of labelled polymers to silica as well as segmental relaxation processes in solutions of acrylic polymers. In the latter case unusual interactions were indicated between the polymers and chlorinated hydrocarbon solvents. Fluorescence analysis of hydrophobically modifled cellulose have shown the operation of slow dynamic processes while fluorescence... 

One parameter related to CMC is Krafft temperature, or critical micelle temperature. This is the minimum temperature at which surfactants form micelles. Below the Krafft temperature, there is no value for the critical micelle concentration that is, micelles cannot form. 

Figure 4.5 Solubility of an amphilic drug at different temperatures in a phosphate buffer, illustrating the effect on solubility at the micelle formation at the critical micelle temperature (CMT).

The cloud point is the temperature at which the detergent precipitates in watery solution. A number of further concepts that are less important to daily work—such as the critical micelle temperature, the Krafft point, and the hydrophile/lipophile equilibrium— are described in the overview article by Helenius and Simons (1975), which is the best piece of writing about detergents in spite of its age. 

Another example of multicompartment micellar IPECs is the macromolec-ular co-assembly of the triblock terpolymer poly(Af,Af-dimethylacrylamide)- /ocfc-poly(A-acryloylalanine)-fetocA -poly(iV-isopropylacrylamide) or the diblock terpolymer poly(A,A-dimethylacrylamide)-fe/(9cA -poly(Ai-isopropylacrylamide)-stat-(A-acryloylvaline), interacting in aqueous media with poly(ar-vinylbenzyl) trimethylammonium chloride (PVBTAC) [76, 77], The authors demonstrated that interpolyelectrolyte complexation of such assemblies formed with PVBTAC within specific pH and temperature ranges makes them stable with respect to the disassembly induced by cooling below critical micellization temperatures. 

The kinetics of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymers have been intensively studied by T-jump experiments with light scattering detection [115, 126-130]. PEO-PPO-PEO triblock copolymers form micelles in aqueous solution, with PPO as the core forming hydrophobic block. Above the critical micelle concentration (cmc) and critical micelle temperature there exists a transition region of AT 10-15 C where... 

Another example of schizophrenic behavior has been observed in the case of A-b-(B-co-C) DHBCs. The copolymers P(EGMA-co-MMA)-PDEA (with various contents of MAA) associated in water either at elevated temperature and low pH values or at low temperature and increased pH values [28], Inverse micelles were observed in each case. Moreover, both the solution salinity and the content of MAA had a great influence on the critical micellization temperature, as was revealed by the experimental observations. 

The catalytic activity of PVim containing DHBCs has been also demonstrated [23]. A PNIPAM-PVim copolymer was foimd to form micelles with PNIPAM cores at elevated temperatures. The above micelles showed catalytic activity toward the hydrolysis of p-nitrophenyl acetate. Interestingly, molecular dissolved copolymer chains do not show the same catalytic activity. The Arrhenius plot for the PVim-based DHBCs exhibited a pronounced upward curvature above the critical micellization temperature. 

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